Device in which a light beam marks the x-ray beam



Oct. 4, 1960 P. CAMFFERMAN 2,955,205

DEVICE IN WHICH A LIGHT BEAM MARKS THE X-RAY BEAM I Filed July 21, 1958////////////////////,7/////AV/J///A7////////fi7/// mrllualllvalvnfllnuuuarll. vnuum (Mann MIIAIII-A 1".

INVENTOR. PAUL US CAMF F ERMAN AGE attachment casting shadows.

United States Patent W DEVICE m WHICH A LIGHT BEAM MARKS THE X-RAY BEAMPaulns Camfierman, Eindhoven, Netherlands, assignor to North AmericanPhilips Company, Inc., New York, N.Y., a corporation of Delaware FiledJuly 21, 1958, Ser. No. 749,677

Claims priority, application Netherlands July 22, 1957 4 Claims. (Cl.250-64) Accurate adjustment of the X-ray tube in therapeutic irradiationand in making radiographs can be performed in a simple manner by the useof a device in which a light beam marks the X-ray beam. For thispurpose, a source of light is disposed so that the virtual origin of thelight rays coincides with the focus of the X-ray tube. The light beam islimited by the screening envelope for the X-rays so that the light raysilluminate the same area which is irradiated by the X-rays. Thus, if thesize of the irradiation field is to be changed, the angle of aperture ofthe X-rays can be adjusted by using the change in size of theilluminated area, without the use of a fluorescent screen.

In order to avoid undesirable shadows in the X-ray image, the source oflight cannot be arranged in the X-ray beam. It is disposed at the sideof this beam. Provision is further made of an inclined plane mirror todeflect the light in the direction of the beam axis of the X-rays. Themirror is disposed in front of the X-ray window and consists of a thinreflecting metal layer applied to a support made of a material whichabsorbs the X-rays slightly only, for example, a transparent syntheticresin such as the material which is commercially available under thetrademark Plexiglas. The X-ray absorption cannot be entirely avoided sothat in this arrangement the amount of radiation supplied by the X-raytube is slightly diiferent from the amount which is really supplied to apatient or is used for exposing a photographic plate or film.

The amount of radiation produced by the X-ray tube is measured by meansof an ionization chamber. This chamber must be arranged in the X-raybeam and, even if a small ionization chamber is used, not only causes acertain absorption but also casts some shadows, mainly of the means ofattachment by which the ionization chamber is secured in the screeningenvelope for the X-rays.

It is known to measure the amount of radiation by means of an ionizationchamber which is arranged in front of the window of the X-ray tube andis secured to the tube housing. This arrangement requires the use of anionization chamber which is suitable for attachment to the tube housingwhile the housing must be provided with means of attachment.

It is an object of the present invention to avoid these specialprovisions and the disadvantage of the means of The invention relates toan arrangement in which a light beam marks the beam emitted by an X-raytube by means of a light source and at least one mirror, the light ofthe light source, which is arranged at the side of the X-ray window ofthe tube, being deflected in the direction of the beam axis of theX-rays while provision is made of an ionization chamber for measuringthe X-rays. According to the invention, the light rays from the lightsource are deflected by a reflecting surface the support of which supports the ionization chamber also.

The absence of separate securing and supporting means 2,955,205 PatentedOct. 4,

for the ionization chamber renders the construction of such anarrangement simple and cheap. Furthermore, the radiation absorption canbe diminished by combining certain components. For this purpose, one ofthe electrodes of the ionization chamber can be the reflecting layer orpart of this layer, the wall which is more remote from the focal spot ofthe X-ray tube and is coatedwith this layer being transparent.

In order that the invention may readily be carried out, one embodimentthereof will now be described, by way of example, with reference to theaccompanying drawings, in which:

Fig. 1 shows an X-ray tube provided with an arrangement in accordancewith the invention, and

Fig. '2 shows the support of the reflecting surface.

Fig. 1 is a longitudinal sectional view of part of an X-ray tube 1provided with an anode 2 and a cathode 3. This cathode includes afilament 4 while the anode is provided with a target 5 for interceptingthe electrons which are emitted by the filament 4 and accelerated by theaction of an electric potential set up between the anode and thecathode. The electrons concentrate onto the target 5 to forma focal spotand this is the focus of the X-ray beam which passes through an aperture7 in the wall of the envelope 6. Along the circumference of the aperture7 the wall of the envelope 6 has a thickened part 8 in which a circularrecess 9 is made. A flange 10 of a cone 11 fits in the recess. Athreaded securing ring 12 serves to fix the cone 11.

An aperture 13 of the cone 11 irnits the cross-sectional area of theX-ray beam. In the space enclosed by the cone wall provision is made ofan ionization chamber 14. The chamber is secured to supports 15 and 16.The way in which the ionization chamber 14 is secured to these supportsis not of importance. A choice can be made from a variety ofarrangements, for example attachment by screws, springs or clamps. Theionization chamber 14 is a flat member comprising two plane Walls 17 and18 spaced from each other by a narrow space. This space is bounded alongthe circumference of the plates 17 and 18 by a rim 19. The chamber canbe filled with air at atmospheric pressure. The chamber walls are madefrom a material which has a slight radiation absorption, preferably asynthetic resin of the kind made from phenolic resins.

At the side more remote from the source of radiation the wall 17 of thechamber 14 is provided with a smooth reflecting metal layer 22, forexample a deposit of a metal having a high reflective power, for examplesilver or aluminium. Aluminium has a smaller X-ray absorption thansilver and is also more attractive because the reflecting layer is lessreadily damaged. Preferably the reflecting layer 22 is applied to theinner side of the wall 17, and thus lies within the ionization chamber,the surface engaging the wall 17 being reflecting.

The ionization chamber 14 is inclined with respect to the axis of theX-ray beam so that a light ray from a light source 20 which is directedto the point at which the axis of the X-ray beam intersects thereflecting layer, is reflected in the direction of the beam axis 21. Ifthe mirror is provided internally on the wall 17, which consequentlymust be made from a transparent material, for example Plexiglas, somelight losses occur since the light rays twice penetrate the wall. Thisis less objectionable than the additional X-ray losses produced by theuse of a mirror provided externally since in this event the X-rays mustpass through the two electrodes of the ionization chamber andsubsequently through the reflecting metal layer. The opposite wall 18 ofthe ionization chamber 14 is coated with a conductive layer which isalso used as an electrode. Since this layer does not serve as a mirrorfor the light rays, it can be made A 72,955,205 a Y a .of a substancewhich has a slighter absorption for X-rays than metal, for examplecarbon. 7

In Fig. 2 the wall 17 of the ionization chamber is shown which presentsits inner surface to the direction of view. "Phat surface is coated witha-metalilayter-ZZ which $11 the side engagingythe wall .is reflecting.An annular portion 23 lot the .metal layer is removed. In order.toobtain correct measuring results independent of the area which isradiated by the ,X-rays a relatively small portionof the reflectinglayer functions ,as .an electrade -;of the ionizationchamber. It shouldpreferably be smaller than the smallest area to which the X-ray beamwill :16 eflectively reduced. Therefore a centre portion 26, which isnot distinguished from the reflecting layer, is one ,;electrode of theionization chamber. A conductive strip 26, which is also separated fromthe remaining metal coating 22 by an intermediate space 25, isconductively connected to the electrode 24 and serves for the connectionofqone terminalof a voltage source which supplies the potentialdifference required for the ionization chamber.

Whatisclaimed is:

:17. X-ray apparatus comprising an X-ray tube including a target fromwhich Xerays emanate and a Window for transmission of the X-rays, vanionization chamber disposed between the windowofthe X-ray tubeand anobject ,to be irradiated by the X-rays for measuring the intensity ofX-rays to which said object is exposed, a light source for illuminatingthetpath of X-rays between the ionization chamber and the object, and alight reflector at leasta portion of which is an electrode of saidionization chamber constituting one wall of said ionization chamber forreflecting light from said light source into said X-ray path, said lightreflector comprising a supporting member transparent to X-rays and athin light reflecting metal layer transparent to X-rays but opaque tolight.

2. X-ray apparatus as claimed in claim 1 in which the light reflector isthe wall of the ionization chamber remote from the target of the X-raytube.

3. "X-ray apparatus comprising an X-ray tube including a target fromwhich X-rays emanate and a window for transmission ,of the ,X-rays, anionization chamber disposed between the windowof the X-ray tube and anobject to be irradiated by the X-rays for measuring the intensity ofX-rays to which said object is exposed, a light source for illuminatingthe path of X-rays between the ionization :chamber and the object, saidionization chamber having .one wall remote from the target and in thepath of X-rays constituted of a light-transparent material, and alight-reflective metal layer on the inner surface of said wallconstituting an electrode for said ionization chamber and a reflectingsurface for said light source whereby the path of X-rays to said objectis illuminated by light reflected by said metal layer.

'4. X-ray apparatus as claimed in claim 3 in which the said Wall of theionization chamber is constituted of a transparent synthetic resin.

References Cited in the file of this patent UNITED STATES PATENTS1,976,179 Manul Oct. 9, 1934 2,190,200 Victoreen Feb. 13, 1940 2,225,044George Dec. 17, 1940 2,699,505 ;Zieler Ian. 11, 1955

